Process for cleaning, stripping, and polishing metal surfaces



Sep 30, 1947- T. E. BURKHARDT 4 PROCESS FOR CLEANING, STRIPPING, AND POLISHING METAL SURFACES Filed Sept. 25, 1940 IIIII],IIIIIIII/III/II/I/II/IIII,

ATTORNEYS Patented Sept. 30, 1947 PROCESS FOR CLEANING, STRIPPING, AND POLISHING METAL SURFACES Thomas E. Burkhardt, Dayton, Ohio, assignor to General Motors Corporation, Dayton, Ohio, a corporation of Delaware Application September 25, 1940, Serial No. 358,327

4 Claims.

This invention relates to a process for cleaning,

' stripping and polishing metal surfaces.

Heretofore, highly alkaline solutions such as sodium orthosilicate solutions have been used for electrolytically cleaning metal surfaces. It was found that such processes did not perform a sufficiently good job of cleaning and removing the oxide and scale. Also because of the high alkalinity of these solutions the workmen associated with these processes frequently suffered from skin diseases. These highly alkaline solutions were also objectionable since they attack the paint and enamel upon the parts to be cleaned. Furthermore, this and similar processes do not lend themselves readily to automatic conveyorized mechanized operation because the films that are built up during the transfer from one tank to another are not removed by such a cleaning process and become a source of trouble.

It is an object of my invention to provide a process of cleaning including removing oxide and scale from metal surfaces which is more thorough and which is less injurious to workmen employed thereon.

It is another object of my invention to provide a process of cleaning and/or removing oxide and scales from metal surfaces which will be efl'ective when used in automatic conveyorized mechanized operation.

It is another object of my invention to provide a process of cleaning and/or removing oxide and scale from metal surfaces of articles in which paint and enamel on the articles cleaned will not be attacked.

It is still another object of my invention to i provide a process of cleaning and/or removing oxide and scale from metal surfaces which will also polish the metal surfaces.

It is another object of my invention to provide a process for cleaning and polishing cast iron and steel surfaces which will also remove copper therefrom.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawing, wherein a preferred form of the present invention is clearly shown.

In the drawings the figure illustrates, partly diagrammatically, one form of apparatus which may be used to carry out my improved process.

I have found that by the use of phosphates in conjunction with other means, such as a wetting agent, or electric current, or a suitable acid or any combination of these, metal surfaces may be cleaned almost absolutely free of all traces of oxide and scale. Preferably my process employs an electrolyte formed of a low alkaline solution having a pH value less than 10.5, preferably a low alkaline phosphate solution such as one se- 5 lected from a group consisting of tetrasodium pyrophosphate, sodium metaphosphate and sodium hexametaphosphate. This electrolyte is kept at a fairly high temperature and the metallic surfaces to be cleaned are immersed in the electrolyte. The electrolyte is kept in agitation either by the movement of the metallic surfaces through the electrolyte or by some other suitable means.

The process may be performed either anodically or cathodically, but preferably the current is passed from the metallic surfaces as anodes to a suitable cathode in contact with the electrolyte. To obtain more rapid action a suitable wetting agent, a suitable acid or both may be included in'the electrolyte. In some cases the process may go be used non-electrolytically.

Referring now to the drawing, there is shown an overhead conveyor including a chain 22 carrying a plurality of hooks 24 insulated from the conveyor for supporting articles to be elec- 2s trolytically cleaned and polished. The articles include a sealed unit type compressor 28 having cast iron and steel surfaces to be cleaned, an aluminum tray 28, a copper plate 30, and a cast iron reciprocating compressor 32. These are car- 30 ried through the electrolyte 34 contained in a tank 36 of some suitable material such as metal or earthenware.

The electrolytic bath is provided with a suitable cathode 38 of some suitable material such as as copper, iron or nickel. This cathode 38 is connected to a source of power, shown diagrammatically as a battery 40' for passing current from the articles 26, 28, 30 and. 32 as anodes through the electrolyte 34 to the cathode 38. This is ac- 40 complished by connecting the other terminal of the battery to a contact .bar 42 which the supports 44 for the hooks 24 contact when the articles are in the bath in order to complete the circuit. The contact portions 44 are insulated from the conveyor by the insulating sections 48. The conveyor, when in operation, lowers the articles into the bath, connects them to thelsource of power, and moves the articles through the bath so as to cause agitation of the electrolytic bath 5!) adjacent the metal surface tobe cleaned. Afterwards the articles are removed from the bath and carried into rinsing tanks and other such means;

' Preferably, the electrolyte comprises an aqueous per gallon of tetra- It has been found desolution of from 2 to 10 oz. 44 sodium pyrophosphate.

3 sirable to add a suitable wetting agent to the electrolyte. This increases the rapidity of the cleaning and/or removal of oxide and scale. However, this is not absolutely necessary for the success of the process. Throughout the electrolytic treatment, the electrolyte is maintained at a temperature of between, 180 and 210 F. or more. The current used is preferably at a potential of from 7 to 12 volts.

Copper, copper alloys, nickel, aluminum and similar metal surfaces may be thoroughly cleaned and polished by this process. When operated anodically, this process not only thoroughly cleans the exposed metal surfaces but it also polishes them. This action is particularly noticeable upon copper and copper alloys. Where only traces of iron oxide and rust are present upon the iron and steel surfaces, these are also thoroughly cleaned and polished in this solution. Furthermore this process may also be used for removing immersion or electro-chemical deposits of copper on iron and steel at the same time the iron and steel parts are being cleaned anodically, since the copper is removed from the iron and steel as a part of their anodic cleaning process.

When more than traces of oxide coatings or rust are present upon iron and steel surfaces, it is desirable to use about oz. per gallon of tetrasodium pyrophosphatein the electrolyte together with an amount sufficient to reduce the pH value to about 9 of an acid, such as acetic, citric, phosphoric, sulfuric, hydrochloric, nitric, and hydrofluoric acids. This solution may be used electrolytically or in a purely mechanical process. For still heavier oxide coatings, the pH value may be further lowered by the addition of more acid with a lower limit of 7. Likewise for lighter oxide coatings, less acid may be used with an upper limit of 10.5. Such a solution may be used for other metal surfaces.

Immediately following the electrolytic treatment, the articles are rinsed in clean cold running water with cold water sprays; following this, the articles are rinsed in clean soft hot running water at a temperature of 200 F. or more; finally, the articles are dried by air-blasts. After drying, the parts may. be coated with an oil mixture where it is necessary to prevent rusting.

If desired, the electrolyte itself may be agitated by some other suitable means. movement of the articles by the conveyor through the bath may be relied upon to provide suflicient agitation to remove any polarization or similar electrical effect. It is not necessary to use the conveyor or any such means for carrying out this process.

Sodium metaphosphate and sodium hexametaphosphate have somewhat similar properties as tetrasodium pyrophosphate and may be used in its place for cleaning in substantially the same way. Other low alkaline phosphate may also be used. However, tetrasodium pyrophosphate is preferred.

I flnd that, in using this process, certain paints and black enamel, which may be upon the articles, are not attacked. Therefore, this procas may be used for painted and enameled articles which have exposed metal surfaces requiring cleaning. This is a particularly desirable advantage, since occasionally parts, after they have been painted or enameled, require reoperation and require cleaning of this type as a part of the reoperation procedure.

While it is desirable to maintain ,as set forth the specified temperatures, voltages and concen- Otherwise, the

tration, it is possible to use a solution of between 1 and 12 oz. per gallon of tetrasodium pyrophosphate and to keep the temperature as low as 150 F. Also, voltages as low as 2 to 3 volts may be used for cleaning purposes, but for cleaning and polishing it is desirable to use at least 4 volts or more.

While the form of embodiment of the invention as herein disclosed, constitutes a preferred form, it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow.

What is claimed is as follows:

1. The process of electrolytically cleaning, stripping copper from, and polishing the surfaces of ferrous articles which comprises immersing said surfaces in an electrolyte consisting essentially of an aqueous solution of between two and ten ounces per gallon of tetrasodium pyrophosphate maintained at a temperature above 180" F. and passing a direct electric current at a potential between seven and twelve volts from said surfaces as anodes .to a suitable cathode in contact with said electrolyte.

2. The process of electrolytically stripping copper from steel which comprises immersing said steel in an electrolyte consisting essentially of an acidified aqueous solution of an alkali pyrophosphate at a temperature of about F. the pH of the solution being between 9 and 10.5 and passing a direct electric current at a potential of about 3 volts from said steel as anode to a suitable cathode in contact with said electrolyte.

3. The process of electrolytically stripping copper from the surfaces of ferrous metal which comprises immersing said surfaces in an electrolyte consisting essentially of an aqueous solution of between one and 12 oz. per gallon of an alkali pyrophosphate at a temperature between 150 F. and 210 F., passing a direct electric current at a potentialof 3 volts or more from said surfaces as anode to a suitable cathode in contact with said electrolyte, and agitating the electrolyte adjacent said surfaces during the passage of the current.

4. The process of electrolytically polishing copper containing metal surfaces which comprises immersing said surfaces in an electrolyte consisting essentially of an aqueous solution of between 1 and 12 oz. per gal. of an alkali pyrophosphate at a temperature between 150 F. and 210 F., passing a direct electric current at a potential of 4 or more volts from said surface as anode to a suitable cathode in contact with said electrolyte, and agitating the electrolyte ad- Jacent said surfaces during the passage of th current.

THOMAS E. BURKHARDT.

REFERENCES CITED The following references are of record in'the file of this patent:

UNITED STATES PATENTS Number Name Date 1,863,868 McCullough June 21, 1932 1,917,022 Dunn July 4, 1933 2,145,518 Lindh Jan. 31, 1939 2,185,858 Mason Jan. 2, 1940 1,953,998 Truesdale et al. Apr. 10, 1934 2,061,056 Baker et al. Nov. 17, 1938 (Other references on following page) Number Number UNITED STATES PATENTS OTHER REFERENCES Name Date Phosphates, by Gillet, published in the Dunn July 12, 1932 periodical Soap, Jan. 1939, pages 25,. 26 and Delaplace et a1. Aug. 25, 1942 5 69. Preston Sept, 21, 1937 Tetrasodium Pyrophosphate, by Cobbs, pub- Henderson et a1. Apr. 14, 1942 lished in the periodical Soap, Nov. 1938, pages Pullen Jan. 25, 1944 24,25 and 26.

"The Cleaning of Metal, by Mitchell, copy- FOREIGN PATENTS righted 1930 by Magnus Chemical 00., Gar- Country Date wood, N. J., pages 23 and 29 through 51. Great Britain Apr. 28, 1930 Comptes Rendus, vol. 201, pages 1473-5 Great Britain Aug. 2, 1940 (1935). Belgium Mar. 31, 1938 Metal Cleaning and Finishing," vol. 7, No; 1 Italy July 10, 1939 I(Jan.1945),pages 34-36. u Great Britain Sept. 14, 1927 Soap, Aug. 1939, page 59. 

